Littérature scientifique sur le sujet « Minimal model glacier »

AbstractWe propose a simple, highly parameterized model of a tidewater glacier. The mean ice thickness and the ice thickness at the glacier front are parameterized in terms of glacier length and, when the glacier is calving, water depth. We use a linear relation between calving rate and water depth. The change in glacier length is determined by the total change in the mass budget (surface balance and calving flux), but not by the details of the glacier profile and the related velocity field. We show that this may still yield relatively rapid rates of retreat for an idealized bed geometry with a smooth overdeepening. The model is able to simulate the full cycle of ice-free conditions, glacier terminus on land, tidewater glaciers terminus, and backwards. We study two cases: (i) a glacier with a specific balance (accumulation) that is spatially uniform, and (ii) a glacier in a warmer climate with the specific balance being a linear function of altitude. Equilibrium states exhibit a double branching with respect to the climatic forcing (equilibrium-line altitude). One bifurcation is related to the dependence of the calving process on the bed profile; the other bifurcation is due to the height–mass-balance feedback. We discuss the structure of the solution diagram for different values of the calving-rate parameter. The model results are similar to those of Vieli and others (2001), who combined a fairly sophisticated two-dimensional (vertical plane) numerical ice-flow model with the modified flotation criterion suggested by Van der Veen (1996). With regard to the global dynamics of a tidewater glacier, we conclude that the details of the glacier profile or velocity field are less significant than the bed profile and the relation between the water depth and the calving rate.

Abstract. We study the response of a set of glaciers in the Western Italian Alps to climate variations using the minimal glacier modeling approach, first introduced by Oerlemans. The mathematical models are forced over the period 1959–2009, using temperature and precipitation recorded by a dense network of meteorological stations and we find a good match between the observed and modeled glacier length dynamics. Forcing the model with future projections from a state-of-the-art global climate model in the RCP 4.5 and RCP 8.5 scenarios, we obtain a first estimate for the "expiration date" of these glaciers.

Abstract. Despite the great number and variety of glaciers in southern South America, in situ glacier mass balance records are extremely scarce and glacier–climate relationships are still poorly understood in this region. Here we use the longest (> 35 years) and most complete in situ mass balance record, available for glaciar Echaurren Norte in the Andes at ~34° S, to develop a minimal glacier surface mass balance model that relies on nearby monthly precipitation and air temperature data as forcing. This basic model is able to explain 78 % of the variance in the annual glacier mass balance record over the 1978–2013 calibration period. An attribution assessment indicates that precipitation variability constitutes the most important forcing modulating annual glacier mass balances at this site. A regionally-averaged series of mean annual streamflow records from both sides of the Andes is then used to estimate, through simple linear regression, this glacier's annual mass balance variations since 1909. The reconstruction model captures 68 % of the observed glacier mass balance variability and shows three periods of sustained positive mass balances embedded in an overall negative trend totaling almost −42 m w.eq. over the past 105 years. The three periods of sustained positive mass balances (centered in the 1920s–1930s, in the 1980s and in the first decade of the 21st century) coincide with several documented glacier advances in this region. Similar trends observed in other shorter glacier mass balance series suggest the glaciar Echaurren Norte reconstruction is representative of larger-scale conditions and could be useful for more detailed glaciological, hydrological and climatological assessments in this portion of the Andes.

Abstract. Hansbreen is a well studied tidewater glacier in the southwestern part of Spitsbergen, currently about 16 km long. Since the end of the 19th century it has been retreating over a distance of 2.7 km. In this paper the global dynamics of Hansbreen are studied with a minimal glacier model, in which the ice mechanics are strongly parameterised and a simple law for iceberg calving is used. The model is calibrated by reconstructing a climate history in such a way that observed and simulated glacier length match. In addition, the calving law is tuned to reproduce the observed mean calving flux for the period 2000–2008. Equilibrium states are studied for a wide range of values of the equilibrium line altitude. The dynamics of the glacier are strongly nonlinear. The height-mass balance feedback and the water depth – calving flux feedback give rise to cusp catastrophes in the system. For the present climatic conditions Hansbreen cannot survive. Depending on the imposed climate change scenario, in AD 2100 Hansbreen is predicted to have a length between 10 and 12 km. The corresponding decrease in ice volume (relative to the volume in AD 2000) is 45 to 65%. Finally the late-Holocene history of Hansbreen is considered. We quote evidence from dated peat samples that Hansbreen did not exist during the Holocene Climatic Optimum. We speculate that at the end of the mid-Holocene Climatic Optimum Hansbreen could advance because the glacier bed was at least 50 m higher than today, and because the tributary glaciers on the western side may have supplied a significant amount of mass to the main stream. The excavation of the overdeepening and the formation of the shoal at the glacier terminus probably took place during the Little Ice Age.

Abstract. Hansbreen is a well studied tidewater glacier in the southwestern part of Svalbard, currently about 16 km long. Since the end of the 19th century it has been retreating over a distance of 2.7 km. In this paper the global dynamics of Hansbreen are studied with a minimal glacier model, in which the ice mechanics are strongly parameterised and a simple law for iceberg calving is used. The model is calibrated by reconstructing a climate history in such a way that observed and simulated glacier length match. In addition, the calving law is tuned to reproduce the observed mean calving flux for the period 2000–2008. Equilibrium states are studied for a wide range of values of the equilibrium line altitude. The dynamics of the glacier are strongly nonlinear. The height-mass balance feedback and the water depth-calving flux feedback give rise to cusp catastrophes in the system. For the present climatic conditions Hansbreen cannot survive. Depending on the imposed climate change scenario, in AD 2100 Hansbreen is predicted to have a length between 10 and 12 km. The corresponding decrease in ice volume (relative to the volume in AD 2000) is 45 to 65%. Finally the late-Holocene history of Hansbreen is considered. We quote evidence from dated peat samples that Hansbreen did not exist during the Holocene Climatic Optimum. We speculate that at the end of the mid-Holocene Climatic Optimum Hansbreen could advance because the glacier bed was at least 50 m higher than today, and because the tributary glaciers on the western side may have supplied a significant amount of mass to the main stream. The excavation of the overdeepening and the formation of the shoal at the glacier terminus probably took place during the Little Ice Age.

Abstract. We present a minimal model of the glacier surface mass balance. The model relies solely on monthly precipitation and air temperatures as forcing. We first train the model individually for 15 glaciers with existing mass balance measurements. Based on a cross validation, we present a thorough assessment of the model's performance outside of the training period. The cross validation indicates that our model is robust, and our model's performance compares favorably to that from a less parsimonious model based on seasonal sensitivity characteristics. Then, the model is extended for application on glaciers without existing mass balance measurements, and cross validated using the 15 glaciers above, in order to measure its performance on glaciers not included in the model training. This cross validation indicates that the model retains considerable skill even when applied on glaciers without mass balance measurements. As an exemplary application, the model is then used to reconstruct time series of interannual mass balance variability, covering the past two hundred years, for all glaciers in the European Alps contained in extended format of the world glacier inventory. Based on this reconstruction, we present a spatially detailed attribution of the glaciers' mass balance variability to temperature and precipitation variability.

Abstract. We present a minimal model of the glacier surface mass balance. The model relies solely on monthly precipitation and air temperatures as forcing. We first train the model individually for 15 glaciers with existing mass balance measurements. Based on a cross validation, we present a thorough assessment of the model's performance outside of the training period. The cross validation indicates that our model is robust, and our model's performance compares favorably to that from a less parsimonious model based on seasonal sensitivity characteristics. Then, the model is extended for application on glaciers without existing mass balance measurements. We cross validated the model again by withholding the mass balance information from each of the 15 glaciers above during the model training, in order to measure its performance on glaciers not included in the model training. This cross validation indicates that the model retains considerable skill even when applied on glaciers without mass balance measurements. As an exemplary application, the model is then used to reconstruct time series of interannual mass balance variability, covering the past two hundred years, for all glaciers in the European Alps contained in the extended format of the world glacier inventory. Based on this reconstruction, we present a spatially detailed attribution of the glaciers' mass balance variability to temperature and precipitation variability.

AbstractA minimal model of a tidewater glacier based solely on mass conservation is compared with two one-dimensional numerical flowline models, one with the calving rate proportional to water depth, and the other with the flotation criterion as a boundary condition at the glacier terminus. The models were run with two simplified bed geometries and two mass-balance formulations. The models simulate the full cycle of length variations and the equilibrium states for a tidewater glacier. This study shows that the branching of the equilibrium states depends significantly on the bed geometry. The similarity between the results of the three models indicates that if there is a submarine undulation at the terminus of a tidewater glacier, any model in which the frontal ice loss is related to the water depth yields qualitatively the same non-linear behaviour. For large glaciers extending into deep water, the flotation model causes unrealistic behaviour.

Abstract. Evolution of glaciers in response to climate change has mostly been simulated using simplified dynamical models. Because these models do not account for the influence of high-order physics, corresponding results may exhibit some biases. For Haig Glacier in the Canadian Rocky Mountains, we test this hypothesis by comparing simulation results obtained from 3-D numerical models that deal with different assumptions concerning physics, ranging from simple shear deformation to comprehensive Stokes flow. In glacier retreat scenarios, we find a minimal role of high-order mechanics in glacier evolution, as geometric effects at our site (the presence of an overdeepened bed) result in limited horizontal movement of ice (flow speed on the order of a few meters per year). Consequently, high-order and reduced models all predict that Haig Glacier ceases to exist by ca. 2080 under ongoing climate warming. The influence of high-order mechanics is evident, however, in glacier advance scenarios, where ice speeds are greater and ice dynamical effects become more important. Although similar studies on other glaciers are essential to generalize such findings, we advise that high-order mechanics are important and therefore should be considered while modeling the evolution of active glaciers. Reduced model predictions may be adequate for other glaciologic and topographic settings, particularly where flow speeds are low and where mass balance changes dominate over ice dynamics in determining glacier geometry.

Abstract. Despite the great number and variety of glaciers in southern South America, in situ glacier mass-balance records are extremely scarce and glacier–climate relationships are still poorly understood in this region. Here we use the longest (> 35 years) and most complete in situ mass-balance record, available for the Echaurren Norte glacier (ECH) in the Andes at ∼ 33.5° S, to develop a minimal glacier surface mass-balance model that relies on nearby monthly precipitation and air temperature data as forcing. This basic model is able to explain 78 % of the variance in the annual glacier mass-balance record over the 1978–2013 calibration period. An attribution assessment identified precipitation variability as the dominant forcing modulating annual mass balances at ECH, with temperature variations likely playing a secondary role. A regionally averaged series of mean annual streamflow records from both sides of the Andes between ∼ 30 and 37° S is then used to estimate, through simple linear regression, this glacier's annual mass-balance variations since 1909. The reconstruction model captures 68 % of the observed glacier mass-balance variability and shows three periods of sustained positive mass balances embedded in an overall negative trend over the past 105 years. The three periods of sustained positive mass balances (centered in the 1920s–1930s, in the 1980s and in the first decade of the 21st century) coincide with several documented glacier advances in this region. Similar trends observed in other shorter glacier mass-balance series suggest that the Echaurren Norte glacier reconstruction is representative of larger-scale conditions and could be useful for more detailed glaciological, hydrological and climatological assessments in this portion of the Andes.

Mountains are sentinels of climate change, for their rapid response to environmental modifications (UN A/Res/62/196). The possibility of amplified warming in high-altitude regions and the associated notion of Elevation Dependent Warming, although dependent on the specific geographical area and mountain chain considered, is a topic of current interest and debate. Mountain glaciers are rapidly retreating in most of the world, especially evident on the southern side of the European Alps, where large amounts of ice mass have been lost in the last fifty years. This scenario create the condition to develop theoretical simulation model, assessing glacier response to climate change. To obtain estimates of future glacier conditions, quantitative descriptions of dynamics are adopted. The more complex models provide a detailed and realistic description of glacier dynamics, but also require a larger amount of input data. In case such information is not available, as it is often the case for most mountain glaciers, it could be safer to resort to simplified descriptions that make best use of the existing data. The term Minimal Glacier Model (MGM) indicates a class of models that do not explicitly describe the spatial dependence of the dynamical variables and develop a bulk description of the glacier in terms of glacier-averaged dynamical quantities that depend only on time. The MGMs are a simple but effective way of estimating glacier response to climate change and climate variability. In such approach, the main state variable is glacier length, depends on mean thickness and slope using a numerical experimentation with a Shallow Ice Approximation model. The evolution of the glacier length is obtained from an integrated continuity equation driven by the glacier mass balance. In this work, we adopt a description based on the MGM approach with an intensive use of Geographical Information System GIS to set parameters and geomorphological conditions. Moreover, we analysed the climate condition of Alpine region and we considered temperature and precipitation variables as climate forcing to drive the mass balance input. The aim of my Ph.D research program is to apply MGM – GIS approach with climate drivers on all glaciers of Greater Alpine Region with usable mass balance dataset. The final results are the assessments of glacier retreat until 2100, classifying average values. First of all, I used such enhanced MGM approach to investigate the dynamics of two important glaciers on the southern side of the Alps: the Careser glacier (Ortles-Cevedale group, Eastern Italian Alps), and the Rutor glacier (Aosta Valley, Western Italian Alps). After comparing the model results with the available data, I tried to estimate the future behavior of these two glaciers, using the Global Climate Models (GCM) from the CMIP5 project, considering two Representative Concentration Pathways RCP 4.5 and RCP 8.5 to include the most dramatic and the most conservative scenarios still plausible. At a later stage, I have to apply MGM on all glaciers of the GAR: I used precipitation and temperature data from E-OBS dataset, the first high-resolution gridded dataset of daily climate observations over Europe, by the European Climate Assessment & Dataset (ECA&D). Then, to drive the MGM for future climate conditions, I used the NASA Earth Exchange Global Daily Downscaled Projections (NEX-GDDP) dataset: a downscaled climate scenarios for the globe that are derived from the GCM runs conducted under the CMIP5. The simulated average assessments are classified following the geographical location of glaciers, their mass balance trends, their geomorphological parameters (altitude, slope) and the different climate behaviors on the entire GAR.

I. An original methodological discussion is proposed on the problem of the typology of tropical rain forest’s plant communities, based on the study of forest types across gradients of continentality and elevation, within Atlantic central Africa. These investigations were based on the statement that the main problems in forest typology are related to the non-zonal or zonal character of the different vegetation types and to non considering the relations and differences between forest strata.

II. Field data consisted in phytosociological homogeneous sample plots localized within different recognized phytogeographical entities, in a region of tropical Africa where these entities are known to be well conserved. A total of 37 such plots were inventoried in the region extending from the littoral forests of Ndoté, Equatorial Guinea, which are wet evergreen forests, to the continental forests of the Dja, Cameroon, known as evergreen seasonal forests. The studied region also included the oriental Atlantic forests of Equatorial Guinea, known as moist evergreen forests or caesalp forests. In various parts of this continentality gradient, some plots were localized within climax non-zonal formations, namely the submontane rain forests. The emphasis was put on the vegetation of the Monte Alén National Park.

The sampling methodology was willing to be as "complete ", including all strata, "quantitative ", enumerating all individuals, and "representative ", within each stratum, as possible. These multi-layers plots were realised using nested sub-plots, with a sampling size of 100 individuals for every ligneous stratum recognized (dominant trees, dominated trees and shrubs) and a sampling size of 200m² for the herbaceous and suffrutex stratum.

Forest types were defined independently for each stratum and the differences were analysed. A method was proposed for the simultaneous analysis of all floristic data, converting and standardizing the values from ligneous strata, on the one hand, and from understorey strata, on the other hand.

III. Ten forest types were described using IndVal and discussed in the general context of the guineo-congolian region, from a syntaxonomic view point (agglomerative classification) and from a phytogeographical view point (divisive classification). Homologies between these two approaches are described. The proposed phytogeographical system is based on an "open " conception of hierarchical classifications, combining advantages of agglomerative and divisive classifications. In concrete terms, the non-zonal criteria, for example the submontane variants, are categorised separately and in analogy with the zonal criteria, related to the usual phytochoria.

Analysis of ecological relationships for the 10 communities showed that the main variables related to the floristic variability in our mainland rain forests are elevation, rainfall, hygrometry (estimated using bryophytes cover levels) and distance to the ocean. The two extremes on the vertical microclimatic gradient, dominant trees stratum and herbaceous stratum, give similar typologies, however canonical analysis showed that for the herbaceous layer, non-zonal variables (hygrometry and elevation) were gaining more importance when the influence of the two zonal variables was attenuated. In every case, spatial autocorrelation was less important than the environment in explaining floristic variability but its role increased in the spatial arrangement of understorey species, whose dispersal capacity is generally lower than canopy trees. The phytosociological, phytogeographical and ecological description of forest types is accompanied by a physiognomical description using biological types spectrum, as well as architectural models, leaf sizes, etc.

With regard to diversity, we have demonstrated that species richness was higher from upper to lower strata because of the accumulation in lower strata of species from various strata. On the other hand, the proper stratum diversity, i.e. the structural set, decreased from dominant trees to shrubs. The proper diversity of the herb layer showed relatively high figures mainly due to the higher individual density in relation to the existence of microstrata. Within the 37 sample plots, 1,050 taxa have been identified to species or morpho-species levels, for a total of 25,750 individuals. These taxa represent 442 genus among 104 families. The richest forest type is found on the foothills of the Niefang range, on the windward side. This forest type is also characterised by a high number of oligotypic genus and by species belonging to functional types indicators of glacial refuges. These functional types are defined on the basis of the dispersal capacity and on kind of stand needed for effective germination. We formulated the hypothesis that this kind of "foothills refuge ", characterised by his zonal nature, could have been one of the rare refuges for species from mainland rain forests, while montane and fluvial refuges would mainly have preserved species from non-zonal forest types: (sub)montane and riverine.

Based on indicator species of submontane forests, a potential distribution map of this forest type has been realised at the Atlantic central African scale. More than 400 submontane forest localities have been mapped. These forests begin at 400m of altitude near the ocean, and progressively at higher altitude for increasing distance to the ocean. Many lowland localities also comprised submontane species, which could indicate the existence of ecological transgressions. These transgressions would allow migratory tracks for submontane species between isolated mountain ranges, not only during glacial periods, through heights at the northern and southern borders of the congo basin, but also contemporarily through the lowland riverine forest network, in the centre of this basin. Finally, a special attention has been attributed to littoral forests and to some cases of choroecological transgressions, coupled to the ecological equalization phenomenon.

Doctorat en sciences agronomiques et ingénierie biologique
info:eu-repo/semantics/nonPublished

As a unique and high gigantic plateau, the Tibetan Plateau (TP) is sensitive and vulnerable to global climate change, and its climate change tendencies and the corresponding impact on regional ecosystems and water resources can provide an early alarm for global and mid-latitude climate changes. Growing evidence suggests that the TP has experienced more significant warming than its surrounding areas during past decades, especially at elevations higher than 4 km. Greater warming at higher elevations than at lower elevations has been reported in several major mountainous regions on earth, and this interesting phenomenon is known as elevation-dependent climate change, or elevation-dependent warming (EDW).At the beginning of the 21st century, Chinese scholars first noticed that the TP had experienced significant warming since the mid-1950s, especially in winter, and that the latest warming period in the TP occurred earlier than enhanced global warming since the 1970s. The Chinese also first reported that the warming rates increased with the elevation in the TP and its neighborhood, and the TP was one of the most sensitive areas to global climate change. Later, additional studies, using more and longer observations from meteorological stations and satellites, shed light on the detailed characteristics of EDW in terms of mean, minimum, and maximum temperatures and in different seasons. For example, it was found that the daily minimum temperature showed the most evident EDW in comparison to the mean and daily maximum temperatures, and EDW is more significant in winter than in other seasons. The mean daily minimum and maximum temperatures also maintained increasing trends in the context of EDW. Despite a global warming hiatus since the turn of the 21st century, the TP exhibited persistent warming from 2001 to 2012.Although EDW has been demonstrated by more and more observations and modeling studies, the underlying mechanisms for EDW are not entirely clear owing to sparse, discontinuous, and insufficient observations of climate change processes. Based on limited observations and model simulations, several factors and their combinations have been proposed to be responsible for EDW, including the snow-albedo feedback, cloud-radiation effects, water vapor and radiative fluxes, and aerosols forcing. At present, however, various explanations of the mechanisms for EDW are mainly derived from model-based research, lacking more solid observational evidence. Therefore, to comprehensively understand the mechanisms of EDW, a more extensive and multiple-perspective climate monitoring system is urgently needed in the areas of the TP with high elevations and complex terrains.High-elevation climate change may have resulted in a series of environmental consequences, such as vegetation changes, permafrost melting, and glacier shrinkage, in mountainous areas. In particular, the glacial retreat could alter the headwater environments on the TP and the hydrometeorological characteristics of several major rivers in Asia, threatening the water supply for the people living in the adjacent countries. Taking into account the climate-model projections that the warming trend will continue over the TP in the coming decades, this region’s climate change and the relevant environmental consequences should be of great concern to both scientists and the general public.

This chapter looks at the context and circumstances surrounding the implementation of Argentina’s glacier protection law. We also examine the gaps that exist in the implementation of the law and activities that groups like the Center for Human Rights and Environment (CEDHA)—an Argentine nonprofit environmental organization—have carried out to push for this implementation. It’s a long chapter with lots of different activity and so I’ve divided it up into sections that group sets of issues. The first section will look at the context for implementation, the legal attacks by the mining sector and the provinces against the glacier law and how, in this case, CEDHA organized to address these challenges. The second section looks at how, in the absence of information from the state, CEDHA went about carrying out unofficial glacier inventories to draw attention to the risks glaciers and periglacial areas face from industrial activity. The third section looks at analytical work to assess mining impacts to glaciers, as well as complaint actions presented in specific cases where glaciers have been or are being impacted. The passage in the Argentine Senate of the Minimum Standards Regime for the Preservation of Glaciers and Periglacial Environments (law 26.639) on September 30, 2010, was an important stepping stone to achieve a framework and a guiding path for glacier protection in Argentina, but glacier protection was far from a done deal. The glacier law would still have to be regulated and implemented, the key actors responsible for its implementation would have to carry out their responsibilities effectively, and the law would also have to confront systemic legal and political attacks from key detractors, the first two of which had publicly declared themselves strongly against the law and were ready to wage battle: namely Barrick Gold, the mining company that had the most to lose from the implementation of the glacier protection law, and the executive branch of the Province of San Juan who had bet heavily on a development model based on the promotion of mining activity much of which happened to be in glacier and periglacial environments.

The Wapiti River South Slope is located 25 km southwest of Grande Prairie, AB. The slope is 500 m long and consists of a steep lower slope and a shallower upper slope, both of which are located within a landslide complex with ground movements of varying magnitudes and depths. The Alliance Pipelines Ltd. (Alliance) NPS 42 Mainline (the pipeline) was installed in the winter of 2000 using conventional trenching techniques at an angle of approximately 8° to the slope fall line. Evidence of slope instability was observed in the slope since the first ground inspection in 2007. Review of the available geotechnical data indicates two different slide mechanisms. In the lower slope, there is a shallow translational slide within a colluvium layer that is draped over a stable bedrock formation. In the upper slope, there is a deep-seated translational slide within glaciolacustrine and glacial till deposits that are underlain by pre-glacial fluvial deposits. Both the upper and lower slope landslide mechanisms have been confirmed to be active in the past decade. Large ground displacements in the order of several meters between 2012 and 2014 in the lower slope led to a partial stress relief and subsequent slope mitigation measures in the spring and summer of 2014, which significantly reduced the rate of ground movement in the lower slope. Surveying of the pipeline before and after stress relief indicated an increase in lateral pipeline deformation (in the direction of ground movement) following the stress relief. This observation was counter-intuitive and raised questions regarding the effectiveness of partial stress relief to reduce stresses and strains associated with ground movements. Finite element analysis (FEA) was conducted in 2017 to aid in assessing the condition of the pipeline after being subject to the aforementioned activities, and subsequent ground displacement from July 2014 to December 2016. This paper presents the assumptions and results of the FEA model and discusses the effect of large ground displacement, subsequent stress relief and continued ground displacement on pipeline behaviour. The results and findings of the FEA reasonably match the observed pipeline behaviour before and after stress relief. The FEA results showed that while the lateral displacement of the pipeline that was caused by ground movement actually increased following the removal of the soil loading, the maximum pipeline strain was reduced in the excavated portion. The results also indicated that ground displacement in the upper slope following the stress relief had minimal effect on pipe stresses and strains in the lower slope.